Optimisation of oxidants dose for combined chemical and biological treatment of textile wastewater

A test of inhibition of microbial growth of activated sludge in a synthetic textile wastewater under the influence of various oxidants applied in the advanced oxidation process (AOP) pretreatment has been proposed. The inhibitory action of single constituents of the textile wastewater was determined in terms of effective concentration, EC50, for a dyestuff and two detergents employed. The most inhibiting component of the textile wastewater (EC50=28 mg dm−3) appeared to be anthraquinone dyestuff, while the surfactants seemed to be partly biodegradable (EC50=128 mg dm−3 for the softening agent Tetrapol CLB and EC50=1700 mg dm−3 for the anionic detergent Avivage KG concentrate). The application of AOPs prior to biodegradation showed that the most advisable AOP is the ozonation combined with UV radiation or the combination of O3/UV/H2O2. The inhibitory effect of the AOPs on microbial growth during subsequent biodegradation of textile wastewater accounts for only 10%, while untreated wastewater exhibits 47% of inhibitory action. The applied biotest is one of the simplest methods of process optimisation of oxidant or radiation dose for the integrated chemical and biological oxidation of industrial wastewater.